A. Field of the Invention
The present invention relates to circuits for sensing and controlling the level of fluid in a reservoir or similar fluid container.
B. Description of the Prior Art
In fluid systems that include a fluid reservoir for storing fluid, the level of fluid in the reservoir often must be controlled to prevent overflow. Control of the fluid level is often accomplished by an electrical circuit that senses the level of fluid and energizes a pump mounted in the reservoir to pump fluid out of the reservoir thereby maintaining the fluid in the reservoir at a desired level.
Typical prior art procedures employed to accomplish fluid level control include one or more probes adapted to contact the fluid. The probes are typically placed within the reservoir at a lower and an upper position to contact the fluid at different levels in the reservoir. These probes are electrically coupled to a circuit that operates a pump for pumping the fluid out of the reservoir. Since the probes are often submerged for long periods of time, it is also desirable that the probes will not be subjected to plating of contaminants in the fluid. Accordingly, it is preferrable that the probes be coupled to an AC source.
Typical prior art circuits employ one or more complex circuits often including a plurality of probes and, in some instances, circuit elements such as a flip-flop memory and logic channels. An example of this type of prior art control circuit is disclosed in U.S. Pat. No. 3,741,683. Other prior art circuits employ a plurality of transistors and SCR's resulting in a complex circuit. Examples of such a circuit are illustrated in U.S. Pat. No. 3,657,556 and 3,858,102. In addition, prior art circuits may also employ triacs and other expensive elements. An example of this type of prior art circuit is illustrated in U.S. Pat. No. 3,787,733.
Each of these prior art circuits is complex and expensive and, as a result, requires a substantial amount of servicing and are expensive to manufacture.